Processors, memory devices, field-emission-displays, read/write heads and other microelectronic devices generally have integrated circuits with microelectronic components. A large number of individual microelectronic devices are generally formed on a semiconductor wafer, a glass substrate, or another type microelectronic workpiece. In a typical fabrication process, one or more layers of metal are formed on the workpieces at different stages of fabricating the microelectronic devices to provide material for constructing interconnects between various components.
The metal layers can be applied to the workpieces using several techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced deposition processes, electroplating, and electroless plating. The particular technique for applying a metal to a workpiece is a function of the particular type of metal, the structure that is being formed on the workpiece, and several other processing parameters. For example, CVD and PVD techniques are often used to deposit aluminum, nickel, tungsten, solder, platinum and other metals. Electroplating and electroless plating techniques can be used deposit copper, solder, permalloy, gold, silver, platinum and other metals. Electroplating and electroless plating can be used to form blanket layers and patterned layers. In recent years, processes for plating copper have become increasingly important in fabricating microelectronic devices because copper interconnects provide several advantages compared to aluminum and tungsten for high-performance microelectronic devices.
Electroplating is typically performed by forming a thin seed-layer of metal on a front surface of a microelectronic workpiece, and then using the seed-layer as a cathode to plate a metal layer onto the workpiece. The seed-layer can be formed using PVD, CVD or electroless plating processes. The seed-layer is generally formed on a topographical surface having vias, trenches, and/or other features, and the seed-layer is approximately 500-1000 angstroms thick. The metal layer is then plated onto the seed-layer using an electroplating technique to a thickness of approximately 6,000 to 15,000 angstroms. As the size of interconnects and other microelectronic components decrease, it is becoming increasingly important that the plated metal layer (a) has a uniform thickness across the workpiece, (b) completely fills the vias/trenches, and (c) has an adequate grain size.
Electroplating machines for use in manufacturing microelectronic devices often have a number of single-wafer electroplating chambers. A typical chamber includes a container for holding an electroplating solution, an anode in the container to contact the electroplating solution, and a support mechanism having a contact assembly with electrical contacts that engage the seed-layer. The electrical contacts are coupled to a power supply to apply a voltage to the seed-layer. In operation, the front surface of the workpiece is immersed in the electroplating solution so that the anode and the seed-layer establish an electrical field that causes metal in a diffusion layer at the front surface of the workpiece to plate onto the seed-layer.
The structure of the contact assembly can significantly influence the uniformity of the plated metal layer because the plating rate across the surface of the microelectronic workpiece is influenced by the distribution of the current (the xe2x80x9ccurrent densityxe2x80x9d) across the seed-layer. One factor that affects the current density is the distribution of the electrical contacts around the perimeter of the workpiece. In general, a large number of discrete electrical contacts should contact the seed-layer proximate to the perimeter of the workpiece to provide a uniform distribution of current around the perimeter of the workpiece. Another factor that affects the current density is the formation of oxides on the seed-layer. Oxides are generally resistive, and thus oxides reduce the efficacy of the electrical connection between the contacts and the seed-layer. Still other factors that can influence the current density are (a) galvanic etching between the contacts and the seed-layer, (b) plating on the contacts during a plating cycle, (c) gas bubbles on the seed-layer, and (d) other aspects of electroplating that affect the quality of the connection between the contacts and the seed-layer or the fluid dynamics at the surface of the workpiece. The design of the contact assembly should address these factors to consistently provide a uniform current density across the workpiece.
One type of contact assembly is a xe2x80x9cdry-contactxe2x80x9d assembly having a plurality of electrical contacts that are sealed from the electroplating solution. For example, U.S. Pat. No. 5,227,041 issued to Brogden et al. discloses a dry contact electroplating structure having a base member for immersion into an electroplating solution, a seal ring positioned adjacent to an aperture in the base member, a plurality of contacts arranged in a circle around the seal ring, and a lid that attaches to the base member. The seal ring is placed in a channel of the base member. In operation, a workpiece is placed in the base member so that the front face of the workpiece engages the contacts and the seal ring. When the front face of the workpiece is immersed in the electroplating solution, the seal ring prevents the electroplating solution from engaging the contacts inside the base member.
U.S. Pat. No. 6,156,167 issued to Patton et al. (Patton) discloses another apparatus for electroplating the wafer surface. The devices disclosed in Patton include a cup having a center aperture defined by an inner perimeter, a compliant seal adjacent to the inner perimeter, contacts adjacent to the compliant seal, and a cone attached to a rotatable spindle. The cup can be formed of an electrically insulating material, such as polyvinylidene fluoride (PVDF) or chlorinated polyvinyl chloride (CPVC). Alternatively, the cup can be formed of an electrically conductive material, such as aluminum or stainless steel. The compliant seal engages a perimeter region of the wafer surface to prevent the plating solution from contaminating the wafer edge, the backside of the wafer, and the contacts. The compliant seal is formed of a relatively soft material, such as VITON (manufactured by DuPont(copyright)) or CHEMRAZ (manufactured by Green Tweed). In operation, a surface of the cone presses against the backside of the wafer to force a perimeter region of the wafer against the compliant seal.
The devices disclosed in Brogden and Patton may entrap bubbles on the plating surface of a wafer at the inner perimeter of the compliant seal. One feature of these devices that inhibits bubbles from flowing off of the plating surface is the xe2x80x9cwell-depth,xe2x80x9d which is defined by the thickness of the seal and the base member that holds the seal. In Brogden, for example, the combined thickness of the seal and the base member appears to be quite large such that it is expected that bubbles will accumulate at the interior perimeter of the seal during operation. It appears that Patton is an improvement over Brogden, but Patton also appears to have a significant well-depth at the inner perimeter of its compliant seal. The depth of the inner perimeter of the cup and the compliant seal in Patton, for example, is disclosed as being approximately 0.147 inch. Therefore, the electroplating apparatus disclosed in Patton are also expected to allow bubbles to accumulate at the inner perimeter of the seal.
The present invention is generally directed toward contact assemblies, electroplating machines with contact assemblies, and methods for making contact assemblies that are used in the fabrication of microelectronic workpieces. The contact assemblies are generally dry-contact assemblies that inhibit the electroplating solution from engaging the contacts or the backside of the workpieces. In one aspect of an embodiment, a contact assembly for use in an electroplating system comprises a support member and a contact system carried by the support member. The support member, for example, can be a ring or another structure having an opening configured to receive the workpiece. In one embodiment, the support member is a conductive ring, and the contact system can be coupled to the support member. The contact system can have a plurality of contact members projecting into the opening relative to the support member. The contact members can comprise electrically conductive biasing elements, such as fingers, that have a contact site or a contact tip. The contact members can project inwardly relative to the support member along a radius of the opening, or they can be xe2x80x9csweptxe2x80x9d at an angle to a radius of the opening. The contact members can also be cantilevered spring elements that support the workpiece, and they can have a raised feature configured to engage the seed-layer on the workpiece.
The contact assembly can also include a barrier or shield carried by the support member and an elastomeric seal carried by the shield. In one embodiment, the shield projects from the support member to extend under the contact members and into the opening, and the shield includes a lip region in the opening inward of the contact members. The shield can be a flexible member that has an inner edge inward of the contact sites and a xe2x80x9cboundary linexe2x80x9d between the inner edge and the contact sites. The seal can be an elastomeric seal that is molded or otherwise adhered to the lip region of the shield. In one embodiment, the seal can have a first edge at the inner edge of the shield and a second edge at the boundary line of the shield. The second edge of the seal defines its outer perimeter such that the seal does not extend underneath the contact members in selected embodiments.
In operation, a workpiece is loaded into the contact assembly by inserting the workpiece through the opening of the support member until the plating surface of the workpiece engages the contact sites on the contact members. Because the contact members can be biasing elements that flex, the contact members flex in the direction that the workpiece is moving and slide across the plating surface. This movement of the contacts enhances the interface between the contact sites and the seed-layer on the workpiece even though the plating surface of the workpiece may have vias, trenches and other topographical features. The plating surface also engages the seal, which prevents the electroplating solution from engaging the contact members. The face of the workpiece can then be immersed in an electroplating solution while the contact assembly rotates.
Several embodiments of contact assemblies with elastomeric seals are expected to provide a sufficient seal against the plating surface of the workpiece without entrapping bubbles at the perimeter of the workpiece or sticking to the workpiece after the plating cycle. For example, because the seals in several embodiments do not extend underneath the contact members, they can be thin to reduce the well depth. The well depth in selected embodiments can be less than 0.085 inch. Additionally, the width of the seals is limited to a seal zone between the contact sites and the inner edge of the shield to reduce the surface area of the seal that contacts the perimeter of the wafer. This inhibits the workpiece from sticking to the contact assembly after the plating cycle and allows more area on the plating surface to be available for components.